In general, the use of inflatable crash bags for protecting drivers and passengers involved in vehicular accidents is widely known.
In early versions of such devices, a compressed gas such as air, carbon dioxide, or nitrogen was stored, in situ, in a pressure bottle or flask, the valving of which was activated by sensing means responsive to rapid change in velocity or direct impact.
Generally speaking, such devices have been found unsatisfactory because of slow crash bag-inflation rates and the problem and expense of maintaining a pressure bottle or flask at the required pressure level over an indefinite period of time.
As a result, stored gas systems have now been generally replaced by gas-producing compositions, particularly ignitable (exothermic) gas-generating propellant compositions.
A system of the latter type must have a relatively short reaction time (10-60 milliseconds) to achieve the desired degree of bag inflation. In addition, it is very important that (a) the generated gas be essentially non-toxic and non-corrosive; (b) the exothermic reaction occur at a controlled rate to avoid generation of excessive heat capable of weakening or burning the crash bag, or passenger; (c) the propellant composition must retain both stability and reactivity for relatively long periods of time under at least normal driving conditions, including a wide range of ambient temperatures; and (d) the amount of propellant, its packaging and the bag itself must be very compact, light and storable within a steering column and/or dash panel.
Currently, most crash bag propellants contain an azide salt, or similar component capable of producing nitrogen or other inert gas when reacted with an oxidizer component.
Propellants compositions known to the art include, for instance, an alkali metal azide combined with an alkali metal oxidant, with an amide or tetrazole (U.S. Pat. No. 3,912,561); silicon dioxide with an alkali or alkaline earth metal plus a nitrite or perchlorate (U.S. Pat. No. 4,021,275); an alkali metal azide with a metal halide (U.S. Pat. No. 4,157,648); a plurality of metal azides with metal sulfides, metal oxides and sulfur (U.S. Pat. No. 3,741,585); an alkali earth metal plus an azide with a peroxide, perchlorate or nitrate (U.S. Pat. No. 3,883,373); an alkali metal azide with a metal oxide (iron, titanium or copper) (U.S. Pat. No. 3,895,098); an alkali metal-or alkaline earth metal-azide with an oxidant consisting of iron oxide doped with up to 1 wt. % of nickel or cobalt oxide (U.S. Pat. No. 4,376,002); and an alkali-or alkaline earth metal-azide combined with an oxidant obtained by forming a metal hydrated gel of a suitable base and metal salt, which is thereafter dehydrated in the presence of a metal oxide of aluminum, magnesium, chromium, manganese, iron, cobalt, copper, nickel, cerium and various transition series elements (U.S. Pat. No. 4,533,416).
While prior art, as above described and exemplified, covers a wide variety of possible azide/oxidizer compositions capable of producing nitrogen gas, continued efforts are being made to develop still more efficient propellant compositions offering acceptable T/P 50 values (time required to achieve 50% peak pressure) which are also safe (i.e. no intermediate product and components are produced in concentrations which are capable of reacting with acids to form explosive or corrosive intermediates such as copper azide), and (as above noted) which have a sufficiently low heat of reaction to avoid damage to the crash bag or harm to passengers, and which produce essentially no co-generated carbon monoxide gas.
It is an object of the present invention to develop a propellant composition and system which better achieves the above-enumerated goals and characteristics.
It is a further object to substantially reduce or eliminate the need for free metal oxides within oxidant components of crash bag propellants, particularly those capable of producing unstable metal azide intermediates.
It is still a further object to minimize the formation of fines and cracks in pelletized propellant compositions attributable to the presence of high concentrations of metal oxides in the propellent composition.